Anemones Gone Fission

Aggregating anemones are the most abundant species of anemone along the North American coast. Found attached to rocks, they prey on small fish, snails, crabs and other animals that they immobilize with venom from their tentacles, then devour through their mouths, located at the top center of their bodies.

Individuals are just an inch or so in size but, as their name suggests, aggregating anemones grow in masses, and so can be mistaken for a single, much-larger animal. And they have an interesting way of reproducing: they clone themselves by splitting apart in a process called fission.

In the wild, this form of asexual reproduction tends to take place from August to February—researchers believe that may be because food supplies are reduced at those times of year, compared to the more abundant months of April through August.

Infographic of anemones splitting


How does the process of fission work? First, the anemone elongates. The pedal disk at the base of its body (by which it attaches itself to the rock) stretches into an hourglass shape—and the animal’s tissue begins to separate at the narrowest point. The separation moves from the base of the anemone’s body and moves upward toward the oral disk, or mouth. The last body part to separate is the sphincter muscle that surrounds the oral disk. In laboratory settings, researchers have documented this process as taking anywhere from three to five days to complete.

After the animal has successfully divided into two halves, each one “folds in” on itself, with the “open” edges coming into contact and fusing together. Through this healing process, the animal is also able to regenerate any missing or damaged internal structures. The division isn’t always successful: researchers sometimes observe incomplete fission, when the anemone begins the separation process and then, for unknown reasons, reverts to its single form.

In the wild, aggregating anemones often have bright streaks of green in their tentacles and oral disks—that’s the result of photosynthetic algae. Here at the Seattle Aquarium, these animals are a yellow/cream color due to a lack of that algae. Come take a look and learn more (maybe you’ll be lucky enough to spot an animal in the process of dividing!) at the Life on the Edge exhibit on your next visit.

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